Detectives were sceptical of George Zimmerman's account of his shooting of the Florida teenager Trayvon Martin when they interviewed him shortly after the fatal encounter, documents released by prosecutors on Tuesday reveal.

But although they found several inconsistencies in Zimmerman's explanations, they felt they could not be "corroborated or refuted by independent witnesses", leading to the release of the neighbourhood watch leader without charge.

The new revelations come in a police report filed by Sanford police department detective Chris Serino on 26 February, the night the unarmed Martin, 17, was killed. The episode prompted weeks of public protests.

Zimmerman, who was charged six weeks later with second-degree murder after the appointment of a special prosecutor, insisted he acted in self-defence because he said Martin had confronted him.

Zimmerman also told investigators that he had sought to avoid a confrontation because he claimed he was "afraid" of Martin.

Serino's report, however, shows that he believed that unlikely, and that Zimmerman's actions "were inconsistent with those of a person who has stated he was in fear of another subject".

"The physical dimensions of Trayvon Martin and George Zimmerman, coupled with the absence of any specialised training in hand-to-hand combat between either combatant, did not place Zimmerman in an extraordinary or exceptional disadvantage," Serino wrote.

Zimmerman, Serino said, had "exited his vehicle, in spite of his earlier admission to investigators that he was afraid of Martin, and followed Martin in an effort to maintain surveillance of him".

Serino also pointed out that Zimmerman missed at least two opportunities to identify himself to Martin as a neighbourhood watch volunteer or a concerned resident and "defuse the circumstances surrounding their encounter". Instead, the detective noted, the confrontation was "ultimately avoidable" if Zimmerman had identified himself to Martin or stayed in his car.

Another police observation was that "investigation reveals that Martin was in fact running generally in the direction of where he was staying as a guest in the neighbourhood".

Zimmerman initially admitted following Martin during that 911 call, but later denied having done so. His lawyers claim that their client lost sight of Martin and that the teenager doubled back on him and attacked him, although prosecutors question why a teenager believed to have been running away from a likely confrontation would have returned.

Serino did accept, however, that injuries Zimmerman claimed he received in a fight with Martin – a bruised and bloodied face, a broken nose and cuts to the back of his head – were "marginally consistent with a life-threatening episode as described by him." The report notes that the episode followed Zimmerman's fifth call to police since August to report a suspicious black male in the community.

The detective's comments, many of which were censored from an earlier copy of the report released in May, concluded with Serino's belief that probable cause existed for Zimmerman, 28, be charged with manslaughter – a recommendation rejected by Norman Wolfinger, state attorney for Seminole County.

Also released on Tuesday was a two-hour video of Zimmerman being interviewed at the police station, during which he took a voice-stress test, similar to a lie-detector test. That concluded that he "told substantially the complete truth".

Other material in the discovery package from the office of special attorney Angela Corey included statements and a video of Zimmerman re-enacting the confrontation to detectives, which was previously released publicly by defence lawyer Mark O'Mara last week.

Zimmerman, who is in the Seminole County jail, is scheduled to appear before Judge Kenneth Lester in Sanford on Friday to ask for bail. He was previously freed in April but rearrested earlier this month when the judge ruled he lied about donations made to his private website.

His wife Shellie Zimmerman, 25, was charged with perjury for claiming at his first bail hearing that she had no knowledge of a fund estimated by prosecutors to be worth more than $135,000.